A power-supply device that supplies power to a load device is necessary for products that include such devices.
In many cases, the load device (e.g., LCD, CCD, LSI) is developed concurrently with the development of the product. Therefore, there are often cases where the specifications (e.g., desired voltage, load current) desired by users are not decided until the final stage of development.
Further, in the power-supply device, it is necessary to confirm a gain, a phase margin and the like, by also taking into account external components. Commonly, these parameters are confirmed by simulation. A simulation allows the power-supply circuit to be developed with parameters that have been confirmed beforehand, even before a prototype of the load device becomes available. This is advantageous in providing a sufficient development period for the power-supply circuit.
Further, Patent Document 1 (Japanese Unexamined Patent Publication No. 74456/1992 (Tokukaihei 4-74456) (published on Mar. 9, 1992)) described below teaches a fabrication method of a power-supply device, in which a plurality of power-supply circuits are provided in advance in a semiconductor, and only a necessary circuit block among these power-supply circuits is connected in accordance with user's specifications. With the method, the development is completed by simply changing metals, and therefore it is possible to shorten the time for producing the prototype.
However, in the arrangement in which simulation is employed to assess operations of the power-supply device and the load device, it is difficult to perform the simulation with enough accuracy.
Specifically, simulation requires modeling of external components for simulation, and modeling of the load device. However, since it is difficult to establish a model for a coil or other external components for simulation, and a model for transient current characteristics of the load device, a simplified model has currently been used to perform simulation for the operation assessment during development. In the case where the load device is under development, procedures such as the extraction of a load model for the device need to be made on the basis of provisional specifications. However, the specifications used in these procedures often differ from the actual specifications of the device.
Accordingly, it is difficult to perform a sufficiently accurate simulation for the operation assessment of the power-supply device and the load device. As a preventative measure for the risk of causing problems due to error, there have been attempts to provide a compensating circuit for proving a margin, or install a dummy element in the chip so as to allow for correction of error in a short time period by changing metals. However, this often increases the chip size, with the result that production costs may be increased, or the products may not be able to have a strong competitive edge.
On the other hand, in the method of Patent Document 1 that a device is developed by changing wirings, a finished product include an unnecessary circuit that is not used. In this case, the size of the chip cannot be reduced, and therefore the production costs may increase.
Meanwhile, the load devices currently require a wide range of voltages, some requiring a small voltage to comply with the finer design rule, and others still requiring the conventional voltage.
This increases the number of channels in the output lines (the number of output lines to supply power), from the point of view of the power-supply device. Accordingly, the problem of increased production cost becomes more prominent, as compared to the case where only a power-supply circuit for one channel is provided.